Aging implicates a progressive decline in muscle mass and strength (sarcopenia) which is counteracted by strength training, and a decline of aerobic performance (muscle fatigability, reduced aerobic capacity and loss of mitochondrial power or OXPHOS capacity in muscle tissue). OXPHOS capacity is increased or maintained high by a life style involving endurance exercise and strength training [1]. Life style changes from the age of 20-30 years to the elderly, but is subject to change and intervention. Depending on group selection in cross-sectional studies, OXPHOS capacity declines from the age of 20-30 years [2,3], or is independent of age up to 80 years [4,5]. Independent of age, there is a strong decline of OXPHOS capacity in human vastus lateralis from BMI of 20 to 30 [6]. The relationship between BMI, training and OXPHOS capacity is also observed in horse skeletal muscle [7]. At a BMI >30, a minimum OXPHOS capacity is reached in human v. lateralis that may be characteristic of a low-grade inflammatory state (‘mitochondrial fever’). Onset of degenerative diseases (diabetes 2, neuromuscular degeneration, various cancers) and mitochondrial dysfunction interact in an amplification loop progressing slowly with age, such that cause and effect of mitochondrial dysfunction cannot be distinguished. Diminished antioxidant capacity at low mitochondrial density is an important mechanistic candidate in the state of mitochondrial fever.